# Stepping to the beat

You are watching a marching band practice outdoors. Near you are two trumpet players, one marching directly towards you and one away from you at the same speed. Each trumpet player is playing an A (440 Hz) and you hear a beat between the two sounds at a frequency of 2 Hz. How fast are the trumpet players marching in m/s?

Details and assumptions

• The speed of sound is $340~\mbox{m/s}$.
• The trumpet players aren't moving very fast.
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